JTAG circuit transferring data between devices on TMS terminals

ABSTRACT

The present disclosure describes using the JTAG Tap&#39;s TMS and/or TCK terminals as general purpose serial Input/Output (I/O) Manchester coded communication terminals. The Tap&#39;s TMS and/or TCK terminal can be used as a serial I/O communication channel between; (1) an IC and an external controller, (2) between a first and second IC, or (3) between a first and second core circuit within an IC. The use of the TMS and/or TCK terminal as serial I/O channels, as described, does not effect the standardized operation of the JTAG Tap, since the TMS and/or TCK I/O operations occur while the Tap is placed in a non-active steady state.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 USC §119(e) (1) of provisionalapplication No. 60/534,298, filed Jan. 5, 2004.

This application is related to U.S. patent application Ser, No.10/983,256, filed Nov. 4, 2004, which is incorporated herein byreference. This application claims priority from provisional applicationNo. 60/534,298, filed Jan. 5, 2004.

BACKGROUND OF THE DISCLOSURE Field of the Disclosure

This disclosure relates in general to circuit designs, and in particularto an improvement in the design of IEEE 1149.1 Tap interfaces of ICs andcore circuits for improved communication of test, debug, emulation,programming, and general purpose I/O operations.

Today's ICs may contain many embedded 1149.1 Tap architectures (Tapdomains). Some of these TAP domains are associated with intellectualproperty (IP) core circuits within the IC, and serve as accessinterfaces to test, debug, emulation, and programming circuitry withinthe IP cores. Other TAP domains may exist in the IC which are notassociated with cores but rather to circuitry in the IC external of thecores. Further, the IC itself will typically contain a TAP domaindedicated for operating the boundary scan register associated with theinput and output terminals of the ICs, according to IEEE std 1149.1.

FIG. 1 illustrates a simple example of an IEEE 1149.1 Tap domain 102.The Tap domain includes a Tap controller 104, an instruction register(IR) 106, at least two data registers (DR) 108, and multiplexercircuitry 110. The Tap domain interface consists of a TDI input, a TCKinput, a TMS input, a TRST input, and a TDO output. In response to TCKand TMS control inputs to Tap controller 104, the Tap controller outputscontrol to capture data into and shift data through either the IR 106from TDI to TDO or a selected DR 108 from TDI to TDO. The data shiftedinto IR 106 is updated and output on bus 114 to other circuits, and thedata shifted into a DR 108 is updated and output on bus 112 to othercircuits. DR 108 may also capture data from other circuits on bus 112and IR 106 may capture data from other circuits on bus 114. In responseto a TRST input to the Tap controller 104, the TAP controller, IR and DRare reset to known states. The structure and operation of IEEE 1149.1Tap domain architectures like that of FIG. 1 are well known.

FIG. 2 illustrates the state diagram of the Tap controller 104. All IEEE1149.1 standard Tap controllers operate according to this state diagram.State transitions occur in response to TMS input and are clocked by theTCK input. The IEEE 1149.1 Tap state diagram is well known.

FIG. 3 illustrates an example system where a number of Tap domain 102interfaces of ICs 306-312 or embedded cores 306-312 within ICs areconnected together serially, via their TDI and TDO terminals, to form ascan path 302 from TDI 304 to TDO 306. Each Tap domain 102 of theICs/cores 306-312 are also commonly connected to TCK 314, TMS 316, andTRST 318 inputs. The scan path's TDI 304, TDO 306, TCK 314, TMS 316, andTRST 318 signals are coupled to a controller, which can serve as a test,debug, emulation, in-system-programming, and/or other applicationcontroller. While only four Tap domains 102 of ICs/cores 306-312 areshown, any number of IC/core Tap domains may exist in scan path 302, asindicated by dotted line 322. The scan path 302 arrangement of IC/coreTap domains is well known in the industry.

As seen in FIG. 3, if data is to be input to Tap domain 102 of IC/core312 from controller 320 it must serially pass through all leading Tapdomains of ICs/cores 306-310. Further, if data is to be output from Tapdomain 102 IC/core 306 to controller 320 it must pass through alltrailing Tap domains of ICs/cores 308-312. Thus a data input and outputlatency exists between Tap domains of ICs/cores in scan path 302 andcontroller 320. As will be seen later, the present disclosure provides away to eliminate this data input and output latency by making use of thedirect TMS 316 and/or TCK 314 connections between the Tap Domains ofICs/cores 306-312 and controller 320. Having a direct connection fordata input and output between the controller 320 and the Tap domains102, via the TMS and/or TCK connections, provides improved datacommunication throughput during test, debug, emulation,in-circuit-programming, and/or other type of operations. Further, usingthe direct TCK and/or TMS connections for data input and output betweencontroller 320 and Tap domains 102 only involves the controller and thetargeted Tap domain. Non-targeted Tap domains are not aware of oraffected by the direct TMS and/or TCK communication.

SUMMARY OF THE DISCLOSURE

The present disclosure provides a method and apparatus of communicatingdata between; (1) an IC in a scan path and a controller of the scan pathusing the standard direct TMS and/or TCK connections that exists betweenthe IC and controller, (2) a first IC of a scan path and a second IC ofthe scan path using the direct TMS and/or TCK connections between thelOs, (3) a first core circuit of a scan path in an IC and second corecircuit of the scan path of the IC using the direct TMS and/or TCKconnections between the cores. The TMS and/or TCK data I/O communicationoccurs while the Tap controller of the Tap domains of the IC/core are ina non-active state. Thus the TMS and/or TCK I/O communication does notdisturb or modify the state of Tap domains of the IC/core in a scanpath. The TMS and/or TCK I/O communication is achieved by addingcircuitry to the IC/core and coupling the circuitry to the TMS and/orTCK terminals of the IC's/core's Tap domain. When enabled by controloutput from the IC's/core's Tap domain, the added circuitry becomesoperable to input data from the Tap domain's TMS and/or TCK terminal oroutput data onto the Tap domain's TMS and/or TCK terminal. Conventionalcontrollers 320 coupled to the TMS and TCK signals are improved,according to the present disclosure, such that they can input data froma Tap domain's TMS and/or TCK terminal and output data to a Tap domain'sTMS and/or TCK terminal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a conventional IEEE 1149.1 Tap domain architecture.

FIG. 2 illustrates the state diagram of a conventional IEEE 1149.1 Tapcontroller.

FIG. 3 illustrates a conventional arrangement of ICs or cores within ICswith their Tap domains connected in a scan path and the scan pathcoupled to a controller.

FIG. 4 illustrates the scan path and controller arrangement of FIG. 3adapted for TMS I/O communication according to the present disclosure.

FIG. 5 illustrates TMS I/O communication circuitry coupled to a Tapdomain according to the present disclosure.

FIG. 6 illustrates the TMS I/O Circuit of FIG. 5 according to thepresent disclosure.

FIG. 7 illustrates circuitry and timing for receiving Manchester encodedTMS input data according to the present disclosure.

FIG. 8A illustrates a Manchester decoder state machine for receivingencoded TMS data according to the present disclosure.

FIG. 8B illustrates a state diagram of the operation of the Manchesterdecoder state machine of FIG. 8A.

FIG. 9 illustrates circuitry and timing for transmitting Manchesterencoded TMS output data according to the present disclosure.

FIG. 10A illustrates a Manchester encoder state machine for transmittingencoded TMS data according to the present disclosure.

FIG. 10B illustrates a state diagram of the operation of the Manchesterencoder state machine of FIG. 10A.

FIG. 11 illustrates how TMS I/O communication can occur while a Tapcontroller is in the Run Test/Idle state according to the presentdisclosure.

FIG. 12 illustrates how TMS I/O communication may occur while a Tapcontroller is in other states according to the present disclosure.

FIG. 13 illustrates TMS I/O communication occurring between and IC and acontroller.

FIG. 14 illustrates TMS I/O communication occurring between two ICs.

FIG. 15 illustrates TMS I/O communication occurring between two corecircuits within an IC.

FIG. 16 illustrates the scan path and controller arrangement of FIG. 3adapted for TCK I/O communication according to the present disclosure.

FIG. 17 illustrates TCK I/O communication circuitry coupled to a Tapdomain according to the present disclosure.

FIG. 18 illustrates the TCK I/O Circuit of FIG. 17 according to thepresent disclosure.

FIG. 19 illustrates circuitry and timing for receiving Manchesterencoded TCK input data according to the present disclosure.

FIG. 20A illustrates a Manchester decoder state machine for receivingencoded TCK data according to the present disclosure.

FIG. 20B illustrates a state diagram of the operation of the Manchesterdecoder state machine of FIG. 20A.

FIG. 21 illustrates circuitry and timing for transmitting Manchesterencoded TCK output data according to the present disclosure.

FIG. 22A illustrates a Manchester encoder state machine for transmittingencoded TCK data according to the present disclosure.

FIG. 22B illustrates a state diagram of the operation of the Manchesterencoder state machine of FIG. 22A.

FIG. 23 illustrates how TCK I/O communication can occur while a Tapcontroller is in the Run Test/Idle state according to the presentdisclosure.

FIG. 24 illustrates how TCK I/O communication may occur while a Tapcontroller is in other states according to the present disclosure.

FIG. 25 illustrates TCK I/O communication occurring between and IC and acontroller.

FIG. 26 illustrates TCK I/O communication occurring between two ICs.

FIG. 27 illustrates TCK I/O communication occurring between two corecircuits within an IC.

DETAILED DESCRIPTION

FIG. 4 illustrates a scan path system 402 of ICs/cores that include Tapdomains plus additional TMS I/O circuitry. The combination of the Tapdomain and TMS I/O circuitry is referred to as TAPIO 416. FIG. 4 issimilar to FIG. 3 in regard to the way the TDI, TDO, TCK, TMS, and TRSTsignals are coupled between the TAPIOs 416 and controller 420.Controller 420 is different from controller 320 in that it has beenimproved according to the present disclosure to include the capabilityof communicating data to and from the TAPIOs 416 via the TMS connection.Controller 420 maintains the conventional ability of controller 320 tocommunicate the Tap domains of the TAPIOs 416 using the standard IEEE1149.1 serial protocol. As seen, the TMS connection between controller420 and TAPIOs 416 is shown as a bidirectional signal path, as opposedto the unidirectional signal path of the TMS connection in FIG. 3. Whena TAPIO 416 is selected for sending data to the controller 420 accordingto the present disclosure, the TMS connection will become an output fromthe TAPIO and an input to the controller. When a TAPIO 416 is selectedfor receiving data from the controller 420 according to the presentdisclosure, the TMS connection will become an output from the controllerand an input to the TAPIO. As can be seen in FIG. 4, data is transferreddirectly between a selected TAPIO 416 and controller 420. Therefore thedata latency problem mentioned in regard with FIG. 3 does not exist inFIG. 4.

Additionally, according to the present disclosure, one TAPIO of anIC/core in the scan path may communicate to another TAPIO of an IC/corein the scan path via the common bidirectional TMS connection. To achievethis mode of operation, the controller 420 selects one TAPIO to transmitand another TAPIO to receive. The controller then disables its TMSoutput driver so that the transmitting TAPIO can output on its TMSterminal to send data to the TMS terminal of the receiving TAPIO. Again,the data is directly transferred between the TAPIOs without theaforementioned latency problem.

FIG. 5 illustrates the TAPIO circuit 416 in more detail. As seen theTAPIO 416 consists of a Tap domain 502, a TMS communication circuit 514,And gates 506-508, and a Clock Source circuit 528. The Clock Source 528can be a clock producing circuit within the IC or it can come from a pinof the IC. Tap domain 502 is similar to Tap domain 102 with theexception that it includes And gate 504 for detecting when the Tapcontroller 104 is in the Run Test/Idle (RTI) state 202 of FIG. 2. TheTap controller 104 is a four bit state machine defining the 16 uniquestates shown in FIG. 2. Each of the 16 Tap states is defined by a uniqueone of the four bit state machine codes. While not shown, the fourinputs of the And gate 504 are inverted or not inverted to allow the Andgate to detect, with a logic high output, when the Tap controller is inthe Run Test/Idle state. For example, if the Run Test/Idle state has afour bit code of 0101, then the “0” inputs to And gate 504 will beinverted such that the And gate will receive all “1's” at its inputs sothat it outputs a logic one when the Tap controller is in the RunTest/Idle state. This will be the case throughout the remainder of thisspecification for all And gates that are described for use in detectingTap controller states. Also while And gates are shown being used todetect Tap controller states, other gating circuits may be used as well.

Further, Tap domain 502 differs from Tap domain 102 in that it includesan Enable TMS Output signal 510 and an Enable TMS Input signal 512. TheEnable TMS Output signal is set whenever the TMS communication circuit514 is to perform a data output operation on TMS. The Enable TMS Inputsignal is set whenever the TMS communication circuit 514 is to perform adata input operation on TMS. As seen, the Enable TMS Input or Enable TMSOutput signals can come, by design choice, from either the IR 106 viabus 114 or from a DR 108 via bus 112.

When Enable TMS Output is set high and when the Tap controller 104 is inthe Run Test/Idle (RTI) state 202, the output of And gate 506 will gohigh to enable the TMS communications circuit 514 to perform a TMSoutput operation. When Enable TMS Input is set high and when the Tapcontroller 104 is in the Run Test/Idle (RTI) state, the output of Andgate 508 will go high to enable the TMS communications circuit 514 toperform a TMS input operation. During either TMS communicationoperation, the Tap controller 104 remains in the Run Test/Idle state202.

TMS communication circuit 514 consists of a Frame Counter 516, And gate520, TMS I/O Circuit 526, Data Source 522, and Data Destination 524. TheFrame Counter 516 is a data register 108 that can be scanned via TDI andTDO by the Tap controller 104 to load a count of the number of dataframes that are to be sent from the Data Source 522 during a TMS outputoperation. A data frame in this disclosure is defined by a fixed numberof transmitted data bits. After being scanned, and when enabled by theoutput of And gate 506, the Frame Counter operates as a counter to countthe number of data frames output on TMS. After all data frames have beensent out on TMS, the count complete (CC) output from the Frame Counterwill go low to halt the TMS output operation of TMS I/O Circuit 526, viaAnd gate 520. And gate 520 is gated on and off by the Enable TMS Outputsignal being high and low respectively. When gated off, the CC outputfrom the Frame Counter cannot inadvertently, say during an 1149.1operation that passes through the Run Test/Idle state, enable the TMSI/O Circuit 526. The Frame Counter receives IR & Tap Control input viabus 530 for scanning in the count, control input 518 from the TMS I/OCircuit 526 for knowing when to count a frame, and a clock input fromthe Clock Source circuit 528.

When enabled for inputting data from TMS, the TMS I/O Circuit 526receives the TMS data and transfers it to the Data Destination circuitry524. Data Destination circuitry 524 may be any circuitry within an ICincluding but not limited to; (1) an address bus, (2) a data bus, (3) aRam memory, (4) a Cache memory, (5) a register file, (6) a FIFO, (7) aregister, (8) a processor, (9) a peripheral circuit, or (10) a buscoupled to circuitry external to the IC.

When enabled for outputting data on TMS, the TMS I/O Circuit 526receives data from the Data Source circuitry 522 and outputs the data onTMS. Data Source circuitry 522 may be any circuitry within an ICincluding but not limited to; (1) an address bus, (2) a data bus, (3) aRam memory, (4) a Rom memory, (5) a Cache memory, (6) a register file,(7) a FIFO, (8) a register, (9) a processor, (10) a peripheral circuit,or (11) a bus coupled to circuitry external to the IC.

FIG. 6 illustrates TMS I/O Circuit 526 in more detail. TMS I/O Circuitconsists of a Data & Clock Decoder 604, Input Register 602, Data & ClockEncoder 614, and Output Register 612. As will be described in moredetail later, the TMS communication is based on Manchester datacommunication whereby the clock and data signals are combined andtransmitted together on TMS.

The function of the Data & Clock Decoder 604 is to receive a frame ofManchester encoded data on TMS terminal 316, extract the data 606 andclock (CK) 608 components from the encoded data, and input the data 606serially to Input Register 602 in response to the extract CK signal 608.Enable (EN) signal 628 enables Input Register 602 to receive the data606. Input Register 602, once filled with a complete serial data frame,outputs the data frame in parallel to Data Destination 524 via data bus622. CK signal 608 and Data In Ready control signal 606 controls theData Destination to receive the parallel data from bus 622. This processof receiving Manchester encoded serial data frames from TMS terminal316, decoding the serial data frames into parallel data patterns, andinputting the parallel data patterns to Data Destination 524 is repeateduntil the TMS input communication operation is completed.

The function of the Data & Clock Encoder 614 is to control the OutputRegister 612, via Enable (EN) 626, CK 618 and Data Output Ready 616signals, to receive parallel data patterns from the Data Source 522 viabus 624 and output the data serially, via Data signal 620, to the Data &Clock Encoder 614. The Data & Clock Encoder 614 encodes the serial inputdata 620 with a clock from Clock Source 528 to produce a frame of serialManchester encoded data to be output on TMS terminal 316. This processof receiving a parallel data pattern from the Data Source 522,converting the parallel data pattern into a frame of serial Manchesterencoded data, and outputting the frame of serial Manchester encoded dataonto TMS terminal 316 is repeated until all the parallel data patternsfrom Data Source 522 have been serially transmitted from TMS terminal316. As seen in FIG. 6, the Data Out Ready signal 616, which controlsthe input of parallel data patterns from the Data Source to the OutputRegister is also input to Frame Counter 516 to control the frame count.The count value in the Frame Counter 516 controls the number of paralleldata patterns that are output as encoded serial frames from TMS 316. TheFrame Counter 516 decrements once per each Data Out Ready signal. Asseen in FIG. 5, when the frame count in Frame Counter 516 expires, theFrame Counter halts the TMS serial output operation by setting the countcomplete (CC) signal low.

FIG. 7 illustrates a timing example of the Data & Clock Decoder circuit604 receiving Manchester encoded data on TMS terminal 316. Manchesterencoding, is well known and operates by sending an encoded signal as apair of opposite bits. In the timing diagram, each pair of opposite bitsare shown within boxes 708. Each box represents a Manchester encodedsignal. In one example of Manchester encoding, an encoded logic one isrepresented by a logic zero bit followed by a logic one bit, and anencoded logic zero is represented by a logic one bit followed by a logiczero bit. An alternate Manchester encoding reverses the polarity of thebit pair for an encoded logic one and encoded logic zero.

As seen the Manchester Decoder circuit 702 in circuit 604, when enabledby Input Enable, becomes operable to receive Start signals 704, fourlogic ones in this example, from TMS 316. More than two consecutivelogic ones is an illegal Manchester bit encode, therefore more than twologic ones can be used as an indication to initialize the ManchesterDecoder for receiving serial frames of encoded TMS data. While two Startsignals, each comprising two logic ones, are shown in this example, moreStart signals may be used if desired. After recognizing the Startsignals, the Manchester Decoder receives frames 1-N of Manchesterencoded serial data from TMS 316. The Manchester Decoder extracts theData and CK components from each Manchester encoded bit in the frame andshifts the extracted Data into the Serial Input Parallel Output (SIPO)Register 602. The Enable output from the Manchester Decoder enable theSIPO Register 602 to receive data. After each frame is decoded andshifted into SIPO Register 602, the Manchester Decoder outputs the DataIn Ready signal to Data Destination 524. In response to the Data InReady signal the Data Destination receives (stores and/or processes) theparallel output of Register 602. This process continues until theManchester Decoder receives Stop signals 706, four logic zeros in thisexample, from TMS 316. More than two consecutive logic zeros is anillegal Manchester bit encode, therefore more than two logic zeros canbe used as an indication to cause the Manchester Decoder to stopreceiving serial frames of encoded TMS data. While two Stop signals,each comprising two logic zeroes, are shown in this example, more Stopsignals may be used if desired.

FIG. 8A illustrates a more detail example of Manchester Decoder circuit702. The Manchester Decoder 702 consists of a Manchester Decoder StateMachine 802 and a Bit Counter 806. The state machine 802 receives theTMS signal from TMS terminal 316, a clock signal from Clock Source 528,the Input Enable signal from And gate 508, and a count complete (CC)signal from Bit Counter 804. The state machine outputs a Data signal toSIPO Register 602, a clock (CK) signal to SIPO Register 602 and DataDestination 524, an Enable signal to SIPO Register 602, the Data InReady signal to Data Destination 524, count control to Bit Counter 804.

FIG. 8B illustrates the operation of state machine 802. When the InputEnable signal is set high, the state machine begins sampling the TMSinput for Start signals 704. The frequency of the Clock Source is setsufficiently high to allow over-sampling of the TMS input signal. AfterStart signals are detected, the state machine begins sampling the TMSinput to decode the Manchester encoded bit pairs 708. Each time a bitpair is decoded, the appropriate Data value is clocked into SIPORegister 602 by the CK signal and the Bit Counter is clocked by countercontrol outputs. During the decode operation, the state machine monitorsthe CC input from the counter 804. When a CC signal is detected,indicating that the number of bits received is equal to a full frame ofbits, the state machine sets the Data In Ready signal high to enable theData Destination to receive the full frame of bits from the paralleloutput from SIPO Register 602. This process continues until the statemachine receives the Stop signals 706 on the TMS signal, indicating theend of the transmission of Manchester encoded data frames. The statemachine transitions to the Stop state and waits for the Input Enablesignal to be set low by the Tap controller 104 exiting the Run Test/Idlestate. A subsequent JTAG scan operation to either the DR 108 or the IR106 register (i.e. the register from which it came) can set the EnableTMS input signal 512 low. When Input Enable goes low, the state machine802 transitions back to the Input Enable state.

FIG. 9 illustrates a timing example of the Data & Clock Encoder circuit614 outputting Manchester encoded data on TMS terminal 316. In thetiming diagram, each Start 704, Data 708, and Stop 706 bit signals areagain illustrated as they were in FIG. 7. As seen the Manchester Encodercircuit 902 in circuit 614, when enabled by Output Enable, becomesoperable to transmit Start signals 704, four logic ones in this example,onto TMS 316. Since the TMS terminal of an IC or Core is normally drivenby a controller 420, the controller must disable its drive of the TMSterminal to allow the TMS terminal of the IC or Core to become an outputto drive the TMS of the controller during TMS output modes of operation.The disabling of the TMS controller output is indicated a “Z” in thetiming diagram.

As seen, a 3-state buffer 904 inside the Manchester Encoder 902 becomesenabled during TMS output operation to drive the TMS terminal of the ICor core. After transmitting the Start signals, the Manchester Encoderloads parallel data into the Parallel Input Serial Output (PISO)Register 612 from the Data Source 522 and starts shifting the PISORegister 612. Each bit shifted from the PISO Register to the ManchesterEncoder is appropriately encoded as a Manchester bit pair signal 708 andtransmitted out of the IC or core via the TMS terminal 316. As seen thetransmission of the Manchester bit pairs begins following the lasttransmitted Start signal. The Manchester Encoder combines the data andclock components together such that a Manchester Decoder 702 in thereceiving controller 420 or other IC/core can extract the componentsback into separate data and clock signals. The Enable output from theManchester Encoder enables the PISO Register 612 to load and shift outdata. The serial data shifted out from one parallel load of the PISORegister forms one serial bit frame. After each frame is shifted out ofthe PISO Register 612, the Manchester Encoder outputs the Data Out Readysignal to PISO Register 612 and Data Source 522. In response to the DataOut Ready signal the PISO Register 612 inputs parallel data from DataSource 522 to began the next serial output frame that is encoded andoutput on TMS 316. This process continues until the Output Enable inputto the Manchester Encoder goes low, at which time the Manchester Encoderoutputs Stop signals 706, four logic zeros in this example, onto TMS 316and disables the output buffer 904, ending the TMS output operation.

FIG. 10A illustrates a more detail example of Manchester Encoder circuit902. The Manchester Encoder 902 consists of a Manchester Encoder StateMachine 1002, Bit Counter 1004, TMS buffer 904, and Clock Divider (CD)906. The state machine 1002 receives the Data output signal from PISORegister 612, a clock signal from Clock Source 528 via Clock Divider906, the Output Enable signal from And gate 520, and a count complete(CC) signal from Bit Counter 1004. The state machine outputs a clock(CK) signal to PISO Register 612 and Data Source 522, an Enable signalto PISO Register 612, a Data Out Ready signal to PISO Register 612 andData Source 522, count control to Bit Counter 1004, and encoded data toTMS 316 via buffer 904.

FIG. 10B illustrates the operation of state machine 1002. When theOutput Enable signal is set high, the state machine enables the outputbuffer 904 and outputs Start signals 704 onto TMS 316. Also the firstparallel data pattern from Data Source 522 is loaded into PISO Register612. After sending the Start Bits, the state machine begins encoding theserial output data shifted from PISO Register 612 into Manchesterencoded outputs on TMS 316. The frequency of the CK output from thestate machine 1002 is sufficiently less than the frequency of the clockoutput from the Clock Divider 906 to allow each data bit shifted out ofPISO Register 612 to be encoded into the appropriate Manchester bit pairsignal 708. Each time an encoded bit pair is output on TMS 316, the BitCounter counts in response to control inputs from state machine 1002.During the encoding operation, the state machine monitors the CC inputfrom the Bit Counter 1004. When a CC signal is detected, indicating thatthe last bit of the current bit frame is being shifted out of PISORegister 612, the Data Out Ready signal is set to cause the nextparallel data pattern from Data Source 522 to be loaded into PISORegister 612 to allow starting the next frame of data bit outputs fromthe Register 612. Each data bit of each new frame of data loaded andshifted out of PISO Register 612 is encoded into Manchester bit pairsand output on TMS 316. This process continues until the state machine1002 detects the Output Enable signal going low, as a result of thecount in Frame Counter 516 expiring and setting its frame count completeCC signal low, which in turn sets the Output Enable signal low via Andgate 520. When Output Enable is detected low, the state machine 1002outputs the Stop signals 706 to indicate to controller 420 or otherIC/core that the transmission of Manchester encoded data frames has cometo an end. The state machine then disables output buffer 904 fromdriving the TMS terminal 316 and transitions to the Output Enable stateof the diagram. When the TMS output operation is ended, the controller420 enables its TMS output, transitions the Tap 104 from the RunTest/Idle state to set the Enable TMS Output signal low by a JTAG scanoperation to either the DR 108 or the IR 106 register from whence itcame.

Preferably the Clock Sources 528 in the transmitting and receivingdevices (i.e. controller 420, IC, or core) are of the same frequency.This would ensure that, by the use of Clock Divider 906 of ManchesterEncoder 902, the data encoded and output from a transmitting device'sManchester Encoder 902 will be at a bit rate easily over-sampled anddecoded by the non-divided Clock Source 528 driving the ManchesterDecoder 702 in a receiving device. A test that TMS data transmitted fromEncoder 902 at the divided Clock Source rate is properly received byDecoder 702 at the full Clock Source rate can be achieved by simplyenabling both circuits in the same device to operate simultaneously totransmit and receive data over their common TMS connection, then checkthat the data received in the Data Destination circuit 524 is correct.

As seen in the TMS Manchester communication timing diagrams of FIGS. 7and 9, the format of a TMS output operation is the same as the format aTMS input operation. Both formats include a header of at least two Startsignals 704 followed by frames of Manchester data signals 708 followedby a trailer of at least two Stop signals 706. This allows simple andstandardized data communication between a TMS transmitting device (i.e.controller 420, IC, or core) and a TMS receiving device (i.e. controller420, IC, or core). Other more complex formats may also be implemented asthe need arises, such as formats that include frames for addressing andcommanding operations to support more sophisticated communication needs.

FIG. 11 illustrates how a TMS I/O operation is initiated by the Tapcontroller transitioning into the Run Test/Idle state 202. Prior totransitioning into the Run Test/Idle state, a scan operation will havebeen performed to set the Enable TMS Output 510 or Enable TMS Input 512signal high, depending upon whether an TMS input or TMS output isdesired. Also if it is a TMS output operation, the Frame Counter 516 isloaded with the frame count value. Once this setup procedure isaccomplished, the Tap controller 104 is transitioned into the RunTest/Idle state as shown in FIG. 11. Once in the Run Test/Idle state,the TCK clock is halted at a low logic level. The RTI signal is setwhich enables And Gates 506 and 508 to pass the Enable TMS Input orOutput signals 510 and 512 to TMS communication circuit 514. Theselected TMS input or TMS output operation begins at time 1102 and isexecuted during time 1104 as shown in FIG. 11 while the Tap is in theRun Test/Idle state with the TCK halted. When the TMS input or TMSoutput operation is competed at time 1106, the TMS and TCK signal mayonce again be operated by the controller 420 to transition the Tapcontroller 104 through its states. As can be seen, with the Tapcontroller in the Run Test/Idle state and with the TCK halted, TMS inputand TMS output operations are completely transparent to the Tapcontroller and all IEEE 1149.1 circuitry connected to the Tapcontroller. While this example halts the TCK at a low logic level, theTCK could be halted at a high logic level as well.

FIG. 12 is provided to illustrate that other Tap controller states,other than Run Test/Idle, may be used to perform TMS input and TMSoutput operations. For example, the Shift-DR state 1202, the Pause-DRstate 1204, the Shift-IR state 1206, and the Pause-IR state 1208 all maybe used in addition to the Run Test/Idle state for TMS input and outputoperation modes. To use these additional Tap controller states as statesin which TMS input and output operations may be performed is simply amatter of providing And gates 1210 to decode when the Tap controller isin one of the states, as And gate 504 did for detecting the RunTest/Idle state, and providing an Or gate 1212 for indicating when anyof the And gate 1210 outputs are high. The output of the Or gate 1212would be substituted for the RTI output of And gate 504 in FIG. 5 andinput to And gates 506 and 508. With this substitution made, the TCKcould be halted in any one of these states to allow the TMS I/Ooperation to be started, executed, and stopped, as was shown anddescribed in regard to the Run Test/Idle state of FIG. 11. While And/Orgating is shown in this example, other gating circuitry types could beused as well to detect the other Tap states.

FIG. 13 illustrates an example of the TMS I/O operation of the presentdisclosure being performed between an IC 1302 of a scan path 402 and acontroller 420 as shown in FIG. 4. If the controller is performing a TMSoutput operation, the IC will be performing a TMS input operation toreceive the data from the controller via the TMS connection. If the ICis performing a TMS output operation, the controller will be performinga TMS input operation to receive the data from the IC via the TMSconnection.

FIG. 14 illustrates an example of the TMS I/O operation of the presentdisclosure being performed between a first 1402 and second 1404 IC of ascan path 402. If IC 1402 is performing a TMS output operation, IC 1404will be performing a TMS input operation to receive the data from IC1402 via the TMS connection. If IC 1404 is performing a TMS outputoperation, IC 1402 will be performing a TMS input operation to receivethe data from IC 1404 via the TMS connection. During these operations,the TMS output of controller 420 of FIG. 4 will need to be disabled toallow the TMS terminal of the outputting IC to drive the TMS connectionbetween the lOs.

FIG. 15 illustrates an example of the TMS I/O operation of the presentdisclosure being performed between a first 1502 and second 1504 corecircuit within an IC of scan path 402. If core 1502 is performing a TMSoutput operation, core 1504 will be performing a TMS input operation toreceive the data from core 1502 via the TMS connection. If core 1504 isperforming a TMS output operation, core 1502 will be performing a TMSinput operation to receive the data from core 1504 via the TMSconnection. During these operations, the TMS output of controller 420 ofFIG. 4, or the output of an internal buffer in the IC being driven bythe TMS output of controller 420 will need to be disabled to allow theTMS terminal of the outputting core to drive the TMS connection betweenthe cores.

In all of the examples in FIGS. 13-15, the TMS I/O data communicationbetween the devices (IC and controller, IC and IC, core and core) isperformed directly and without introducing any communication latency byhaving to pass the communicated data through any other devices. Further,devices not involved in the TMS I/O communication are not effected bythe TMS I/O communication.

FIG. 16 illustrates a scan path system 1602 of ICs/cores that includeTap domains plus additional TCK I/O circuitry. The combination of theTap domain and TCK I/O circuitry is referred to as TAPIO 1616. FIG. 16is similar to FIGS. 3 and 4 in regard to the way the TDI, TDO, TCK, TMS,and TRST signals are coupled between the TAPIOs 1616 and controller1620. FIG. 16 is different from FIG. 4 in that communication is providedbetween the controller 1620 and TAPIO 1616 via the TCK signal 314instead of via the TMS signal 316. Controller 1620 is different fromcontroller 420 of FIG. 4 in that it has been improved according to thepresent disclosure to include the capability of communicating data toand from the TAPIOs 1616 via the TCK connection. As with controller 420,controller 1620 maintains the conventional ability of controller 320 tocommunicate the Tap domains of the TAPIOs 1616 using the standard IEEE1149.1 serial protocol. As seen, the TCK connection between controller1620 and TAPIOs 1616 is shown as a bidirectional signal path, as opposedto the unidirectional signal path of the TCK connection in FIG. 3. Whena TAPIO 1616 is selected for sending data to the controller 1620according to the present disclosure, the TCK connection will become anoutput from the TAPIO and an input to the controller. When a TAPIO 1616is selected for receiving data from the controller 1620 according to thepresent disclosure, the TCK connection will become an output from thecontroller and an input to the TAPIO. As can be seen in FIG. 16, data istransferred directly between a selected TAPIO 1616 and controller 1620.Therefore the data latency problem mentioned in regard with FIG. 3 doesnot exist in FIG. 16.

Additionally, according to the present disclosure, one TAPIO of anIC/core in the scan path may communicate to another TAPIO 1616 of anIC/core in the scan path via the common bidirectional TCK connection. Toachieve this mode of operation, the controller 1620 selects one TAPIO totransmit and another TAPIO to receive. The controller then disables itsTCK output driver so that the transmitting TAPIO can output on its TCKterminal to send data to the TCK terminal of the receiving TAPIO. Again,the data is directly transferred between the TAPIOs without theaforementioned latency problem.

FIG. 17 illustrates the TAPIO circuit 1616 in more detail. As seen theTAPIO 1616 consists of a Tap domain 502, a TCK communication circuit1714, And gates 506-508, a Clock Source circuit 528, and a D flip flop1702. The Clock Source 528 can be a clock producing circuit within theIC or it can come from a pin of the IC. Tap domain 502 is similar to Tapdomain 102 with the exception that it includes the previously describedAnd gate 504 for detecting when the Tap controller 104 is in the RunTest/Idle (RTI) state 202 of FIG. 2, and that it includes an Enable TCKOutput signal 1710 and an Enable TCK Input signal 1712. D flip flop 1702has a data (D) input and a reset (R) input coupled to the output of Andgate 504, an inverted clock input coupled to TCK 314, and a data (Q)output (RTI) coupled to an input of And gates 506 and 508. The EnableTCK Output signal is set whenever the TCK communication circuit 1714 isto perform a data output operation on TCK. The Enable TCK Input signalis set whenever the TCK communication circuit 1714 is to perform a datainput operation on TCK. As seen, the Enable TCK Input or Enable TCKOutput signals can come, by design choice, from either the IR 106 viabus 114 or from a DR 108 via bus 112.

When the Tap controller 104 is in the Run Test/Idle state 202 the outputof And gate 504 will be high, placing a logic one on the data input andthe reset input of D flip flop 1702. With the Tap controller in RunTest/idle, the RTI output of D flip flop 1702 will go high on thefalling edge of TCK via the logic one output from And gate 504. When theTap controller exits from the Run Test/Idle state, the RTI output of Andgate 504 goes low by the output of And gate 504 going low, which resetsthe RTI output of D flip flop 1702 to a logic zero.

When Enable TCK Output is set high and the RTI output of D flip flop1702 is high, the output of And gate 506 will go high to enable the TCKcommunications circuit 1714 to perform a TCK output operation. WhenEnable TCK Input is set high and the RTI output of D flip flop 1702 ishigh, the output of And gate 508 will go high to enable the TCKcommunications circuit 1714 to perform a TCK input operation. Duringeither TCK communication operation, the Tap controller 104 remains inthe Run Test/Idle state 202 since the TMS signal 316 input fromcontroller 1620 will be held low.

The structure and operation of TCK communication circuit 1714 is thesame as TMS communication circuit 514 of FIG. 5 with the exception thatTCK I/O Circuit 1726 has been substituted for TMS I/O Circuit 526.

When enabled for inputting data from TCK, the TCK I/O Circuit 1726receives the TCK data and transfers it to the Data Destination circuitry524. Data Destination circuitry 524 may be any circuitry within an ICincluding but not limited to; (1) an address bus, (2) a data bus, (3) aRam memory, (4) a Cache memory, (5) a register file, (6) a FIFO, (7) aregister, (8) a processor, (9) a peripheral circuit, or (10) a buscoupled to circuitry external to the IC.

When enabled for outputting data on TCK, the TCK I/O Circuit 1726receives data from the Data Source circuitry 522 and outputs the data onTCK. Data Source circuitry 522 may be any circuitry within an ICincluding but not limited to; (1) an address bus, (2) a data bus, (3) aRam memory, (4) a Rom memory, (5) a Cache memory, (6) a register file,(7) a FIFO, (8) a register, (9) a processor, (10) a peripheral circuit,or (11) a bus coupled to circuitry external to the IC.

FIG. 18 illustrates TCK I/O Circuit 1726 in more detail. TCK I/O Circuit1726 is the same as TMS I/O Circuit 526 of FIG. 6 with the exceptionthat it uses the TCK signal 314 for communication instead of the TMSsignal 316.

As described previously in regard to TMS I/O Circuit 526, the functionof the Data & Clock Decoder 604 of FIG. 18 is to receive a frame ofManchester encoded data on TCK terminal 314, extract the data and clock(CK) components from the encoded data, and input the data serially toInput Register 602 in response to the extract CK signal. Input Register602, once filled with a complete serial data frame, outputs the dataframe in parallel to Data Destination 524 via data bus 622. CK signaland Data In Ready control signal controls the Data Destination toreceive the parallel data from bus 622. This process of receivingManchester encoded serial data frames from TCK terminal 314, decodingthe serial data frames into parallel data patterns, and inputting theparallel data patterns to Data Destination 524 is repeated until the TCKinput communication operation is completed.

As described previously in regard to TMS I/O Circuit 526, the functionof the Data & Clock Encoder 614 of FIG. 18 is to control the OutputRegister 612 to receive parallel data patterns from the Data Source 522via bus 624 and output the data serially to the Data & Clock Encoder614. The Data & Clock Encoder 614 encodes the serial input data 620 witha clock from Clock Source 528 to produce a frame of serial Manchesterencoded data to be output on TCK terminal 314. This process of receivinga parallel data pattern from the Data Source 522, converting theparallel data pattern into a frame of serial Manchester encoded data,and outputting the frame of serial Manchester encoded data onto TCKterminal 314 is repeated until all the parallel data patterns from DataSource 522 have been serially transmitted from TCK terminal 314. As seenin FIG. 18, the Data Out Ready signal 616, which controls the input ofparallel data patterns from the Data Source to the Output Register isalso input to Frame Counter 516 to control the frame count. The countvalue in the Frame Counter 516 controls the number of parallel datapatterns that are output as encoded serial frames from TCK 316. TheFrame Counter 516 decrements once per each Data Out Ready signal. Asseen in FIG. 17, when the frame count in Frame Counter 516 expires, theFrame Counter halts the TCK serial output operation by setting the countcomplete (CC) signal to And gate 520 low.

FIG. 19 illustrates a timing example of the Data & Clock Decoder circuit604 receiving Manchester encoded data on TCK terminal 314. The timingexample is the same as that described previously in FIG. 7, with theexception that the TCK signal 314 is used for communication instead ofthe TMS signal 316. Also it is seen that the Input Enable goes high onthe falling edge 1902 of TCK 314. Referring back to FIG. 17, the outputof D flip flop 1702 is set high on the falling edge of TCK 314 when theTap is in the RTI state 202, which in turn sets the Input Enable outputof And gate 508 high if Enable TCK Input 1712 is high. Use of thefalling edge of TCK to initiate the TCK input operation allows theoperation to start after TCK has transitioned to a low logic state whichallows the Start signals 704 (four logic one's in this example) on TCKto be more easily recognized by the Data & Clock Decoder circuit 604.

As seen the Manchester Decoder circuit 702 in circuit 604, when enabledby Input Enable, becomes operable to receive Start signals 704, fourlogic ones in this example, from TCK 316. After recognizing the Startsignals, the Manchester Decoder receives frames 1-N of Manchesterencoded serial data from TCK 314. The Manchester Decoder extracts theData and CK components from each Manchester encoded bit 708 in the frameand shifts the extracted Data into the Serial Input Parallel Output(SIPO) Register 602. The Enable output from the Manchester Decoderenable the SIPO Register 602 to receive data. After each frame isdecoded and shifted into SIPO Register 602, the Manchester Decoderoutputs the Data In Ready signal to Data Destination 524. In response tothe Data In Ready signal the Data Destination receives (stores and/orprocesses) the parallel output of Register 602. This process continuesuntil the Manchester Decoder receives Stop signals 706, four logic zerosin this example, from TCK 314, to cause the Manchester Decoder to stopreceiving serial frames of encoded TCK data.

FIG. 20A illustrates a more detail example of Manchester Decoder circuit702, which is the same as that described in FIG. 8A with the exceptionthat the TCK signal 314 is substituted for the TMS 316 signal. TheManchester Decoder 702 consists of a Manchester Decoder State Machine802 and a Bit Counter 806. The state machine 802 receives the TCK signalfrom TCK terminal 314, a clock signal from Clock Source 528, the InputEnable signal from And gate 508, and a count complete (CC) signal fromBit Counter 804. The state machine outputs a Data signal to SIPORegister 602, a clock (CK) signal to SIPO Register 602 and DataDestination 524, an Enable signal to SIPO Register 602, the Data InReady signal to Data Destination 524, count control to Bit Counter 804.

FIG. 20B illustrates the operation of state machine 802, which is thesame as described previously in regard to FIG. 8B. When the Input Enablesignal is set high, the state machine begins sampling the TCK input forStart signals 704. The frequency of the Clock Source is set sufficientlyhigh to allow over-sampling of the TCK input signal. After Start signalsare detected, the state machine begins sampling the TCK input to decodethe Manchester encoded bit pairs 708. Each time a bit pair is decoded,the appropriate Data value is clocked into SIPO Register 602 by the CKsignal and the Bit Counter is clocked by counter control outputs. Duringthe decode operation, the state machine monitors the CC input from thecounter 804. When a CC signal is detected, indicating that the number ofbits received is equal to a full frame of bits, the state machine setsthe Data In Ready signal high to enable the Data Destination to receivethe full frame of bits from the parallel output from SIPO Register 602.This process continues until the state machine receives the Stop signals706 on the TCK signal, indicating the end of the transmission ofManchester encoded data frames. The state machine transitions to theStop state and waits for the Input Enable signal to be set low by theTap controller 104 exiting the Run Test/Idle state. A subsequent JTAGscan operation to either the DR 108 or the IR 106 register (i.e. theregister from which it came) can set the Enable TCK input signal 1712low. When Input Enable goes low, the state machine 802 transitions backto the Input Enable state.

FIG. 21 illustrates a timing example of the Data & Clock Encoder circuit614 outputting Manchester encoded data on TCK terminal 314. The timingexample is the same as that described previously in FIG. 9, with theexception that the TCK signal 314 is used for communication instead ofthe TMS signal 316. Also it is seen that the Output Enable goes high onthe falling edge 2102 of TCK 314. Referring back to FIG. 17, the outputof D flip flop 1702 is set high on the falling edge of TCK 314 when theTap is in the RTI state 202, which in turn sets the Output Enable outputof And gate 506 high if Enable TCK Output 1710 is high. Use of thefalling edge of TCK to initiate the TCK output operation allows theoperation to start after TCK has transitioned to a low logic state andthe controller 1620 has disabled (“Z”) its TCK output driver.

In the timing diagram, the Start 704, Data 708 (of frames 1-N), and Stop706 signals are again illustrated as they were in FIG. 9. As seen, theManchester Encoder circuit 902 in circuit 614, when enabled by OutputEnable, becomes operable to transmit Start signals 704, four logic onesin this example, onto TCK 314. As mentioned above, the controller 1620will have disabled its TCK output driver to allow the output buffer 904of the Manchester Encoder circuit 902 to drive the TCK 314 terminal.

After transmitting the Start signals, the Manchester Encoder loadsparallel data into the Parallel Input Serial Output (PISO) Register 612from the Data Source 522 and starts shifting the PISO Register 612. Eachbit shifted from the PISO Register to the Manchester Encoder isappropriately encoded as a Manchester bit pair signal 708 andtransmitted out of the IC or core via the TCK terminal 314. TheManchester Encoder combines the data and clock components together suchthat a Manchester Decoder 702 in the receiving controller 420 or otherIC/core can extract the components back into separate data and clocksignals. The Enable output from the Manchester Encoder enables the PISORegister 612 to load and shift out data. The serial data shifted outfrom one parallel load of the PISO Register forms one serial bit frame.After each frame is shifted out of the PISO Register 612, the ManchesterEncoder outputs the Data Out Ready signal to PISO Register 612 and DataSource 522. In response to the Data Out Ready signal the PISO Register612 inputs parallel data from Data Source 522 to began the next serialoutput frame that is encoded and output on TCK 314. This processcontinues until the Output Enable input to the Manchester Encoder goeslow, at which time the Manchester Encoder outputs Stop signals 706, fourlogic zeros in this example, onto TCK 314 and disables the output buffer904, ending the TCK output operation.

FIG. 22A illustrates a more detail example of Manchester Encoder circuit902, which is the same as that described in FIG. 10A with the exceptionthat the TCK signal 314 is substituted for the TMS 316 signal. TheManchester Encoder 902 consists of a Manchester Encoder State Machine1002, Bit Counter 1004, TCK buffer 904, and Clock Divider (CD) 906. Thestate machine 1002 receives the Data output signal from PISO Register612, a clock signal from Clock Source 528 via Clock Divider 906, theOutput Enable signal from And gate 520, and a count complete (CC) signalfrom Bit Counter 1004. The state machine outputs a clock (CK) signal toPISO Register 612 and Data Source 522, an Enable signal to PISO Register612, a Data Out Ready signal to PISO Register 612 and Data Source 522,count control to Bit Counter 1004, and encoded data to TCK 314 viabuffer 904.

FIG. 22B illustrates the operation of state machine 1002. When theOutput Enable signal is set high, the state machine enables the outputbuffer 904 and outputs Start signals 704 onto TCK 314. Also the firstparallel data pattern from Data Source 522 is loaded into PISO Register612. After sending the Start Bits, the state machine begins encoding theserial output data shifted from PISO Register 612 into Manchesterencoded outputs on TCK 314. The frequency of the CK output from thestate machine 1002 is sufficiently less than the frequency of the clockoutput from the Clock Divider 906 to allow each data bit shifted out ofPISO Register 612 to be encoded into the appropriate Manchester bit pairsignal 708. Each time an encoded bit pair is output on TCK 314, the BitCounter counts in response to control inputs from state machine 1002.During the encoding operation, the state machine monitors the CC inputfrom the Bit Counter 1004. When a CC signal is detected, indicating thatthe last bit of the current bit frame is being shifted out of PISORegister 612, the Data Out Ready signal is set to cause the nextparallel data pattern from Data Source 522 to be loaded into PISORegister 612 to allow starting the next frame of data bit outputs fromthe Register 612. Each data bit of each new frame of data loaded andshifted out of PISO Register 612 is encoded into Manchester bit pairsand output on TCK 314. This process continues until the state machine1002 detects the Output Enable signal going low, as a result of thecount in Frame Counter 516 expiring and setting its frame count completeCC signal low, which in turn sets the Output Enable signal low via Andgate 520. When Output Enable is detected low, the state machine 1002outputs the Stop signals 706 to indicate to controller 1620 or otherIC/core that the transmission of Manchester encoded data frames has cometo an end. The state machine then disables output buffer 904 fromdriving the TCK terminal 314 and transitions to the Output Enable stateof the diagram. When the output operation is ended, the controller 1620enables its TCK output and sets the Enable TCK Output signal low by aJTAG scan operation to either the DR 108 or the IR 106 register fromwhence it came.

As with the TMS I/O communication, it is preferable that the ClockSources 528 in transmitting and receiving devices (i.e. controller 1620,IC, or core) be at the same frequency. This would ensure that, by theuse of Clock Divider 906 of Manchester Encoder 902, the data encoded andoutput from a transmitting device's Manchester Encoder 902 will be at abit rate easily over-sampled and decoded by the non-divided Clock Source528 driving the Manchester Decoder 702 in a receiving device. A testthat TCK data transmitted from Encoder 902 at the divided Clock Sourcerate is properly received by Decoder 702 at the full Clock Source ratecan be achieved by performing the test previously describe with the TMSI/O communication.

As seen in the TCK Manchester communication timing diagrams of FIGS. 19and 21, the format of a TCK output operation is the same as the format aTCK input operation. Both formats include a header of Start signals 704followed by frames of Manchester data signals 708 followed by a trailerof Stop signals 706. This allows simple and standardized datacommunication between a TCK transmitting device (i.e. controller 1620,IC, or core) and a TCK receiving device (i.e. controller 1620, IC, orcore). As with the previously described TMS communication of FIGS. 7 and9, TCK communication may be expanded to include other more complexformats as the need arises, such as formats that include frames foraddressing and commanding operations.

FIG. 23 illustrates how a TCK I/O operation is initiated by the Tapcontroller transitioning into the Run Test/Idle state 202. Prior totransitioning into the Run Test/Idle state, a scan operation will havebeen performed to set the Enable TCK Output 1710 or Enable TCK Input1712 signal high, depending upon whether a TCK input or TCK output isdesired. Also if it is a TCK output operation, the Frame Counter 516 isscanned to load the frame count value. Once this setup procedure isaccomplished, the Tap controller 104 is transitioned into the RunTest/Idle state as shown in FIG. 23. Once in the Run Test/Idle state,and after the RTI output of D flip flop 1702 goes high, the selected TCKinput or output operation can begin.

The RTI signal is set high on the falling edge of TCK at time 2302 whichenables And Gates 506 and 508 to pass the Enable TCK Input or Outputsignals 1710 and 1712 to TCK communication circuit 1714. If a TCK outputoperation is to be performed, the controller 1620 will disable its TCKoutput driver after the falling edge of TCK at time 2302 and before time2304 to allow a transmitting device to drive the TCK signal 314. Theselected TCK input or TCK output operation begins at time 2304 and isexecuted during time 2306 as shown in FIG. 23 while the Tap is in theRun Test/Idle state. When the TCK input or TCK output operation iscompeted at time 2308, the TCK signal may once again be driven by thecontroller 1720 to conventionally operate Tap controller 104 using IEEE1149.1 protocols. As can be seen, with the Tap controller in the RunTest/Idle state with TMS held low, TCK input and TCK output operationsare completely transparent to the Tap controllers and all IEEE 1149.1circuitry connected to Tap controllers.

FIG. 24 is provided to illustrate that other Tap controller states,other than Run Test/Idle, may be used to perform TCK input and TCKoutput operations. For example, the Pause-DR state 1204 or the Pause-IRstate 1208 may be used in addition to the Run Test/Idle state 202 forTCK input and output operation modes. To use these additional Tapcontroller states as states in which TCK input and output operations maybe performed is simply a matter of providing And gates 2402 to detectwhen the Tap controller is in one of the states, as And gate 504 did fordetecting the Run Test/Idle state, and providing an Or gate 2404 forindicating when any of the And gate 2402 outputs are high. The output ofthe Or gate 2404 would be substituted for the output of And gate 504 inFIG. 17 as input to D flip flop 1702. The output of D flip flop 1702,renamed “TCK I/O State” in FIG. 24, would maintain its connection to Andgate 506 and 508 as shown in FIG. 17. With this substitution made, theTap controller 104 could be transitioned into any one of these states,and held there by asserting a low on TMS, to allow a TCK I/O operationto be started, executed, and stopped, as was shown and described inregard to the Run Test/Idle state of FIG. 23. While it is possible toalso use the Shift-DR state 1202 and Shift-IR state 1206 for TCK inputand output operations, as was shown and described in the TMS input andoutput operations of FIG. 12, one must be aware that data will beshifting through the lOs/cores of scan path 1602 from TDI to TDO duringthe TCK input or output operations, since the TCK signal will be active.This may or may not be a desired situation and is therefore left up tothe user of the disclosure to determined whether TCK input and outputoperations are also allowed in the Shift-DR and Shift-IR Tap states. Ifallowed, then additional And gates 2402 would be assigned to detectthese additional Tap states and the Or gate 2404 would be equipped withadditional inputs for receiving the outputs from the additional Andgates 2402.

FIG. 25 illustrates an example of the TCK I/O operation of the presentdisclosure being performed between an IC 2502 of a scan path 1602 and acontroller 1620 as shown in FIG. 16. If the controller is performing aTCK output operation, the IC will be performing a TCK input operation toreceive the data from the controller via the TCK connection. If the ICis performing a TCK output operation, the controller will be performinga TCK input operation to receive the data from the IC via the TCKconnection.

FIG. 26 illustrates an example of the TCK I/O operation of the presentdisclosure being performed between a first 2602 and second 2604 IC of ascan path 1602. If IC 2602 is performing a TCK output operation, IC 2604will be performing a TCK input operation to receive the data from IC2602 via the TCK connection. If IC 2604 is performing a TCK outputoperation, IC 2602 will be performing a TCK input operation to receivethe data from IC 2604 via the TCK connection. During these operations,the TCK output of controller 1620 of FIG. 16 will need to be disabled toallow the TCK terminal of the outputting IC to drive the TCK connectionbetween the lOs.

FIG. 27 illustrates an example of the TCK I/O operation of the presentdisclosure being performed between a first 2702 and second 2704 corecircuit within an IC of scan path 1602. If core 2702 is performing a TCKoutput operation, core 2704 will be performing a TCK input operation toreceive the data from core 2702 via the TCK connection. If core 2704 isperforming a TCK output operation, core 2702 will be performing a TCKinput operation to receive the data from core 2704 via the TCKconnection. During these operations, the TCK output of controller 1620of FIG. 16, or the output of an internal buffer in the IC being drivenby the TCK output of controller 1620 will need to be disabled to allowthe TCK terminal of the outputting core to drive the TCK connectionbetween the cores.

In all of the examples in FIGS. 25-27, the TCK I/O data communicationbetween the devices (IC and controller, IC and IC, core and core) isperformed directly and without introducing any communication latency byhaving to pass the communicated data through any other devices. Further,devices not involved in the TCK I/O communication are not effected bythe TCK I/O communication.

While the Manchester encoding and decoding circuits described herein toachieve the TMS and TCK I/O communication have been described as beingstate machines operating synchronous to a clock source 528, thedisclosure is not limited to a particular type of Manchester encodingand decoding circuit. Indeed, other types of Manchester encoding anddecoding circuits may be readily substituted for the example circuitsshown herein and used to achieve the Manchester based TMS and TCK I/Ocommunication objective of the present disclosure.

While the TMS and TCK I/O communication circuit examples were shown asresiding in ICs and/or cores, it should be clear that similar TMS andTCK I/O communication circuits or software that can emulate the TMS andTCK I/O communication circuit functionality also resides in thecontrollers that connect to the ICs and/or cores to enable thecontrollers to communicate with the ICs and/or cores during TMS and TCKI/O communication operations.

Although the present disclosure has been described in detail, it shouldbe understood that various changes, substitutions and alterations may bemade without departing from the spirit and scope of the disclosure asdefined by the appended claims.

1. An electrical system comprising: A. first and second devices eachhaving an IEEE 1149.1 interface including a TDI terminal, a TCKterminal, a TMS terminal, and TDO terminal, the TCK terminals of bothdevices being connected together and the TMS terminals of both devicesbeing connected together; and B. circuit means in each of the first andsecond devices for transferring data between the two devices across theTMS terminals of both devices while a clock signal on the TCK terminalsof the devices is held in a static logical state.
 2. The electricalsystem of claim 1 wherein the first device is an integrated circuit andthe second device is a controller.
 3. The electrical system of claim 1wherein the first device is an integrated circuit and the second deviceis an integrated circuit.
 4. The electrical system of claim 1 whereinthe first device is a core circuit within an integrated circuit and thesecond device is another core circuit within the integrated circuit. 5.The electrical system of claim 1 wherein the data is transferred fromthe first device to the second device.
 6. The electrical system of claim1 wherein the data is transferred from the second device to the firstdevice.
 7. The electrical system of claim 1 wherein the data istransferred using Manchester data bit encoding.
 8. The electrical systemof claim 1 in which the TDO terminal of one device is coupled to the TDIterminal of the other device.
 9. The electrical system of claim 1 inwhich the TMS terminals of both devices normally only receive modeselect signals.
 10. The electrical system of claim 1 in which the TCKterminals normally receive a clock signal to shift data and instructionsbetween the two devices across the TDO and TDI terminals of the twodevices.